1. Field of the Invention
The present invention relates to a wiring structure for a semiconductor device, and more particularly to a wiring structure and formation method thereof for a semiconductor device capable of decreasing a contact resistance by forming a shape provided in a lower portion of a contact hole and undercut into an insulation film.
2. Description of the Prior Art
With a semiconductor circuit increasingly integrated, there is a trend wherein breadth of each conductive wire in semiconductor devices or circuits becomes narrowed.
The decreasing wire breadth in each of the conductive wires also applies to metalization for electrically connecting conductive regions to each other. In addition, the size of a contact hole for contacting a conductive wire to another is decreasing as well.
According to U.S. Pat. No. 4,556,897, during an aluminum applied metallic wiring process a lower and upper wiring layers are contacted to each other in contact holes for maintaining continuity property of aluminum.
However, U.S. Pat. No. 4,556,897 does not provide a solution to an increased contact area and contact resistance when there occurs a misalignment of a mask in forming a contact hole. Besides, it does not apply to a self-aligned contact hole.
With reference to FIG. 1, a conventional wiring structure in a semiconductor device will now be described.
In a portion of the surface of a substrate 1 there is formed a lower conductive layer 2 serving as a conductive wire. After depositing an insulation film 8 on the substrate 1 including the lower conductive wire 2, a contact hole 4 is formed through the insulation film 8 by a selective etching. FIG. 1 also shows a misalignment of the contact hole 4 against the lower conductive layer 2 for a certain reason, which misalignment causes the externally exposed area of the lower conductive layer 2 to be decreased.
Therefore, when there occurs a mask misalignment against the contact hole 4 the area of the conductive wire 2 exposed through the contact hole decreases, whereby the contact resistance increases and accordingly signal transfer in a semiconductor device can be delayed. As a result, the thusly increased resistance may generate current crowing and then electromigration, thereby deteriorating the reliability of a semiconductor device.